1. Field of the Invention
The present invention is generally related to a packaging design for a hydrophone which uses a ceramic substrate with multiple layers of microelectronic circuitry formed thereon to support and connect piezoelectric elements and, more particularly, to a hydrophone which integrates a high gain, frequency compensated, low noise amplifier or other micro-electronics with the acoustic elements without impinging on any required acoustical parameters and which can withstand the crushing pressures of deep water.
2. Description of the Prior Art
Hydrophones, which are underwater sonic receivers, as well as projectors, which are underwater sound transmitting devices, have a wide range of applications. For example, underwater receivers and projectors have been used for seismic exploration, depth finding, navigation, commercial fishing, and for detecting noise from submarines.
Canadian Pat. No. 1,008,554 discloses a buoyant hydrophone for submarine detection which includes a pair of hollow cylindrical transducers formed of piezoelectric ceramic material. The piezo cylinders are symmetrically positioned on opposite sides of a central support made of plastic. The piezo cylinders are radially poled with one cylinder poled positive on its outer surface and negative on its inner surface and the other cylinder being oppositely poled, i.e., negative on its outer surface and positive on its inner surface. Silver electrodes on the inner surfaces of the piezo cylinders may be connected by internal leads to a pre-amplifier that is mounted on the center portion of the central support. Plastic hemispherical shells are positioned on the outer sidewalls of the piezo cylinders for adding strength to the assembled, neutrally buoyant hydrophone. The hydrophone is used in a towed array as opposed to a submerged array.
The Canadian patent refers to the pre-amplifier as an "integral pre-amplifier", but what is meant by this reference is merely that the pre-amplifier is attached to a central portion inside the hydrophone structure. The pre-amplifier is not formed as a unit with the other parts which comprise the hydrophone's structure. It is an add on part which must be separately hand wired to the silver electrodes on the piezo cylinders. Moreover, the specification indicates the pre-amplifier may or may not be required. In addition, the hydrophone is not optimized for acoustic properties.
U.S. Pat. No. 4,228,532 to Sims shows a piezoelectric transducer used in a towed hydrophone array. Two piezoelectric hemispheres and a piezoelectric cylinder are connected together by non-conductive epoxy to form a symmetrical arrangement. The device is not useful at high pressures due to a lack of internal pressure compensation.
U.S. Pat. No. 4,545,041 to Tims et al discloses a shock hardened hydrophone comprising a sensor electrically connected to a low output-impedance pre-amplifier by a circuit board. The sensor includes two metal cups, each cup with a piezoelectric ceramic disk positioned therein for generating a potential difference between the first and second surfaces of the disk. The cups are bolted together with a circuit board positioned between them. A first electrode positioned on both sides of the circuit board is in pressure contact with the first surface of each disk. A wire connects one of the cups to a second electrode positioned on a side of the circuit board. A pre-amplifier is mounted on the circuit board and has input leads soldered to the two electrodes. The input to the pre-amplifier is the voltage difference between the first and second electrodes. The entire sensor-circuitboard-pre-amplifier assembly is potted in polyurethane for waterproofing and bonded to a polyurethane jacketed cable.
Tims et al do not show an integral pre-amplifier in that the pre-amplifiers components are not mounted on the circuit board. The pre-amplifier is placed in a separate pressure housing which is then wired to the circuit board. The circuit board only partially interconnects the acoustic elements. The clamped together configuration of the sensor results in the direct electrical connection of the disks to the metal cups on one surface and to the first electrode on the circuitboard on the other surface. However, the connection between the cups and the second electrode must be accomplished by separate wiring.
There is no teaching in the prior art of an acoustic receiver or projector which includes micro-electronics integral with piezoelectric ceramic elements. There is no teaching in the prior art of using a ceramic substrate which includes micro-electronic circuitry formed thereon to support and connect piezoelectric elements for use in a very high pressure environment.